Liquid crystal display device

ABSTRACT

A liquid crystal display device is provided with a switching element in neighborhoods of crossing points of a gate wiring and a data wiring. An interlayer insulating film is provided on the switching element. A pixel electrode connected with the switching element is provided on the interlayer insulating film. Moreover, a spacer for keeping a thickness of a liquid crystal layer constant is disposed in the liquid crystal layer and in a sealing member for sealing the liquid crystal layer. Materials of the interlayer insulating film and spacers are optimized. This configuration prevents degradation of a defective ratio and reliability due to the spacer disposed in the liquid crystal layer sinking into the interlayer insulating film.

This application is a division of U.S. Ser. No. 08/697,277, filed Aug.27, 1996, now U.S. Pat. No. 6,204,907, issued Mar. 20, 2001.

FIELD OF THE INVENTION

The present invention relates to an active matrix type liquid crystaldisplay device incorporating switching elements, such as Thin FilmTransistors (TFTs), and further relates to a manufacturing method ofsuch a device.

BACKGROUND OF THE INVENTION

FIG. 5(a) is a plan view showing a pixel region of an active matrixsubstrate incorporated in a conventional liquid crystal display device.As shown in FIG. 5(a), the active matrix substrate has a plurality ofpixel electrodes 54 provided in a matrix form. Gate wirings 51 andsource wirings 52 are provided around the pixel electrodes 54 so as toorthogonally cross each other. A TFT 53 is provided in neighborhoods ofcrossing points of the gate and source wirings 51 and 52 as a switchingelement connected to the pixel electrode 54 through a contact hole.

FIG. 5(b) is a cross-sectional view taken along line B—B of the activematrix substrate incorporated in the liquid crystal display device shownin FIG. 5(a). As shown in FIG. 5(b), a gate electrode 61 branching offfrom the gate wiring 51 shown in FIG. 5(a) is provided on a transparentinsulating substrate 60. A gate insulating film 55 is provided to coverthe gate electrode 61. A semiconductor layer 64 is provided on the gateinsulating film 55 above the gate electrode 61. A channel protectionlayer 65 is provided on the center of the semiconductor layer 64. Two n⁺layers 66, respectively serving as a source area and a drain area, areprovided so as to cover both ends of the semiconductor layer 64 and thechannel protection layer 65, and to be separated from each other on thechannel protection layer 65. The n⁺ layers 66 are connected respectivelyto the source electrode 62 branching off from the source wiring 52 andthe drain electrode 63. An interlayer insulating film 59 is provided tocover the TFT 53 and the gate and source wirings 51 and 52 provided inthis manner. The pixel electrode 54 is provided on the interlayerinsulating film 59. The pixel electrode 54 is connected to the drainelectrode 63 of the TFT 53 through the contact hole in the interlayerinsulating film 59.

Finally, the manufacturing process of the conventional liquid crystaldisplay device becomes complete with sealing liquid crystal 58 between aTFT substrate 70 configured in the above manner and an oppositesubstrate 71 equipped with an opposite electrode 56. Here, spacers 57are sandwiched between the TFT substrate 70 and the opposite substrate71 to maintain a predetermined space therebetween (disclosed in JapaneseLaid-Open Patent Application No. 61-156025/1986 Tokukaishou 61-156025).

Polyimide resin is used as the interlayer insulating film 59 in theconventional liquid crystal display device disclosed in the abovelaid-open patent application. However, other highly transparentmaterials, such as acrylic resin, polystyrene and polyester, are alsogenerally used.

Although no disclosure is made about the spacers 57, plastic beads andhard materials, such as glass, are usually used. The plastic bead spaceris generally made of polyimide, epoxy and polystyrene.

Nevertheless, if the above-mentioned acrylic resin is used as theinterlayer insulating film 59 and the spacers 57 are made using epoxyresin, Newton rings are observed in a lighting test after injecting andsealing the liquid crystal (Newton rings are a series of circular brightand dark bands, which look like a wave pattern created on water surfaceby a stone dropping into the water). Especially the phenomenonfrequently occurs in the sealing portion, and the rings were even moreclearly observed with a liquid crystal display device incorporating aninterlayer insulating film in an underlayer of the sealing portion.Consequently, such a liquid crystal display device has problems of ahigh defective ratio and low reliability.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a liquid crystaldisplay device which does not cause Newton rings to occur and which hasa low defective ratio and good reliability.

As a step toward achieving the above object, the inventors of thepresent invention conducted researches to pinpoint causes of Newtonrings, and found out that if acrylic resin is used as an interlayerinsulating film and epoxy resin is used as spacers as in a conventionalliquid crystal display device, the spacers press a pixel electrode, sinkinto the interlayer insulating film, and thus change the space between aTFT substrate and an opposite substrate, thereby causing Newton rings tooccur.

On the contrary, in order to achieve the above object, a liquid crystaldisplay device in accordance with the present invention is configured ina preferred embodiment so that the spacers do not sink into theinterlayer insulating film by optimizing materials of the interlayerinsulating film and spacers. As a result, various problems with theliquid crystal display device using the resin-made interlayer insulatingfilm are successfully solved.

Specifically, in a first preferred embodiment, the liquid crystaldisplay device includes: a liquid crystal layer; a first substrateprovided on one side of the liquid crystal layer; a second substrateprovided on the other side of the liquid crystal layer; and a sealingmember for sealing the liquid crystal layer between the first and secondsubstrates. The liquid crystal layer has therein at least one firstspacer for maintaining a thickness of the liquid crystal layer. Thesecond substrate has: an interlayer insulating film of the same hardnesswith the first spacer or a greater hardness than the first spacer; apixel electrode disposed on one side of the interlayer insulating film;at least one switching element disposed on the other side of theinterlayer insulating film for controlling a display state of a pixel;and a base substrate facing the first substrate through the liquidcrystal layer and the interlayer insulating film.

With the above configuration, the hardness of the interlayer insulatingfilm is either the same as or greater than the hardness of the firstspacer. Therefore, the first spacer can be prevented from sinking in theinterlayer insulating film surface. Newton rings can be thus preventedfrom occurring, which improves reliability and defective ratio inmanufacture of the liquid crystal display device. Moreover, even ifpressure is applied by, for example, a user wiping the liquid crystaldisplay device surface after the liquid crystal display device ismanufactured, the space between the substrates are kept constant. Theliquid crystal display device with high display quality is obtained forthese reasons.

While the interlayer insulating film is formed to have a predeterminedhardness in the above liquid crystal display device, an interlayerinsulating film of a second preferred embodiment is made of elasticbody. The second preferred embodiment is configured in the same manneras the first preferred embodiment, except that a different material isused for the interlayer insulating film. With this configuration, ifpressure is applied to the display surface of the liquid crystal displaydevice, the first spacer sinks in the interlayer insulating film surfaceand the space between the substrates changes temporarily. Nevertheless,as the pressure is removed, resilient power occurs and the spacerecovers to the predetermined space. Therefore, the space between thesubstrates of the liquid crystal display device are kept constant. Theliquid crystal display device with good reliability, a low defectiveratio and high display quality can be provided for these reasons in thesame manner as in the first preferred embodiment.

In either of the liquid crystal display devices of the first and secondpreferred embodiments, the interlayer insulating film is preferably madeof resin having a transmittance in the visible ray area of not less than90%. With this configuration, especially if the interlayer insulatingfilm is incorporated in a transparent type liquid crystal displaydevice, it is possible to obtain beautiful image display with nocoloring. Moreover, since transmittance can be prevented fromdeteriorating, it is possible to restrain increase of power consumptionof the backlight.

Incidentally, in the two embodiments above, the material for theinterlayer insulating film is restricted in terms of hardness orelasticity, compared with prior art. As a result, there occurs a casewhere only an inferior material to conventional materials in terms ofadherence and the like c an b e s elected to satisfy this point.

The following description discusses a preferred method of manufacturinga liquid crystal display device when, for example, the material for theinterlayer insulating film does not have desirable adherence asmentioned above. A method of manufacturing a liquid crystal displaydevice including: a pixel electrode and a switching element fordetermining a display state of a pixel; an interlayer insulating filmdisposed between the switching element and the pixel electrode; and abase substrate provided with the interlayer insulating film, theswitching element and the pixel electrode preferably includes steps of:(1) providing the switching element on the base substrate; (2) providingthe interlayer insulating film on the switching element; (3) improvingfilm property by making an interlayer insulating film surface rough; and(4) providing the pixel electrode on the interlayer insulating film.

The third step includes, for example, a step of ashing treatment orlight radiation in which the interlayer insulating film surface is maderough prior to the fourth step of providing the pixel electrode. As aresult, even if a material of poor surface adherence is used as theresin forming the interlayer insulating film, the interlayer insulatingfilm and the pixel electrode can adhere to each other with no trouble.Note that if the film property improving treatment is ashing treatmentor light radiation treatment, the treatment can be carried out asfollows. If the interlayer insulating film is photosensitive, thetreatment can be carried out at the same time with a process of removingresidue of the photosensitive resin, whereas if the interlayerinsulating film is not photosensitive, the treatment can be carried outat the same time with a process of removing photoresist duringpatterning of the interlayer insulating film. This can avoid an increaseof the number of manufacturing processes, compared with prior art.

Moreover, a method of manufacturing the above liquid crystal displaydevice preferably includes steps of: providing the switching element onthe base substrate; providing the interlayer insulating film on theswitching element; drying the interlayer insulating film with prebakingtreatment before patterning the interlayer insulating film; patterningthe interlayer insulating film; and providing the pixel electrode on theinterlayer insulating film.

With the configuration, the interlayer insulating film is dried withprebaking treatment before pattering the interlayer insulating film.Therefore, it is possible to prevent bad affection, such as dimensionaldistortion when the resin really cures, and to reduce viscosity of theresin forming the interlayer insulating film. Consequently, it ispossible to improve productivity and dimensional accuracy in manufactureof the liquid crystal display device.

Moreover, the inventors of the present invention studied occurrencefrequency of Newton rings with the above conventional liquid crystaldisplay device, and confirmed among other things that Newton ringsfrequently occur in the sealing portion and that the rings were moreclearly observed with a liquid crystal display device incorporating aninterlayer insulating. film in an underlayer of the sealing portion.

On the other hand, in a preferred embodiment, the liquid crystal displaydevice in accordance with the present invention includes: a liquidcrystal layer; a first substrate provided on one side of the liquidcrystal layer; and a second substrate having a base substrate facing thefirst substrate through the liquid crystal layer. On the base substrateof the second substrate, a sealing area is provided outside the displayarea, such as in the periphery of the base substrate. Moreover, aninterlayer insulating film is provided between the base substrate andthe liquid crystal layer, except in the sealing area. At least oneswitching element for controlling a display state of a pixel is providedon one side of the interlayer insulating film, whereas the pixelelectrode is provided on the other side of the interlayer insulatingfilm. In addition, the liquid crystal display device includes a sealingmember, disposed to be in contact with the second substrate in thesealing area, for sealing the liquid crystal layer between the first andsecond substrates.

In the above configuration, the interlayer insulating film is notprovided in the area where the sealing member and the second substrateare in contact with each other. Therefore, the space between thesubstrates can be prevented from varying when the sealing member cures.As a result, it is possible to prevent Newton rings to occur in aneighborhood of the sealing member. Besides, the defective ratio andreliability can be improved in manufacture of the liquid crystal displaydevice.

As an addition to the above configuration, a second spacer is providedin the sealing member to maintain a thickness of the sealing member.Preferably, the second spacer satisfies at least one of the twoconditions: the second spacer (1) is larger in size than the firstspacer and (2) has a greater hardness than the first spacer. With thisconfiguration, the space between the first and second substrates can bemaintained with certainty. Therefore, the liquid crystal display devicewith high display quality can be realized.

In addition, in order to keep the space between the substrates constant,the liquid crystal display device preferably includes a middle film,provided on the sealing area of the base substrate, having betteradherence than the base substrate. With this configuration, theadherence of the sealing member portion is improved, and the highlyreliable liquid crystal display device can be obtained. Moreover, themiddle film is preferably at least one film selected from the groupconsisting of a metallic film, a nitride film and an oxide film. In thiscase, the material for the middle film becomes the same with thematerial for the source wiring of the switching element and the like.Therefore, one process can be shared for forming the switching elementand for forming the middle film, which is especially preferable.

For a fuller understanding of the nature and advantages of theinvention, reference should be made to the ensuing detailed descriptiontaken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1(a) is a plan view showing an arrangement of a pixel region of anactive matrix substrate incorporated in a liquid crystal display deviceof a first embodiment in accordance with the present invention.

FIG. 1(b) is a cross-sectional view taken along line A—A of the activematrix substrate incorporated in the liquid crystal display device shownin FIG. 1(a).

FIG. 2 is an enlarged cross-sectional view showing a neighborhood of asealing portion in a liquid crystal display device of a third embodimentin accordance with the present invention.

FIG. 3 is an enlarged cross-sectional view showing a neighborhood of asealing portion in a variant example of the above liquid crystal displaydevice.

FIG. 4 is an enlarged cross-sectional view showing a neighborhood of asealing portion in another variant example of the above liquid crystaldisplay device.

FIG. 5(a) is a plan view showing a pixel region of an active matrixsubstrate incorporated in a conventional liquid crystal display device.

FIG. 5(b) is a cross-sectional view taken along line B-B of the activematrix substrate incorporated in the liquid crystal display device shownin FIG. 5(a).

DESCRIPTION OF THE EMBODIMENTS

[FIRST EMBODIMENT]

FIG. 1(a) is a plan view showing an arrangement of a pixel region of anactive matrix substrate incorporated in a liquid crystal display deviceof a first embodiment in accordance with the present invention.

As shown in FIG. 1(a), the active matrix substrate has a plurality ofpixel electrodes 4 provided in a matrix form. Gate wirings 1 as scanningwirings and source wirings 2 as signal wirings are provided in anunderlayer of the pixel electrodes 4 so as to surround each of the pixelelectrodes 4 and orthogonally cross each other. Parts of the gate andsource wirings 1 and 2 are provided so as to overlap with a periphery ofthe pixel electrodes 4. A TFT 3 as a switching element is provided in aneighborhood of a crossing point of the gate and source wirings 1 and 2.The TFT 3 may be a switching element such as an MIM(Metal-Insulator-Metal).

In the TFT 3, a gate electrode 31 and a source electrode 32 are providedso as to branch off from the gate wiring 1 and the source wiring 2respectively. A drain electrode 33 is connected to the pixel electrode 4in an upper layer of the drain electrode 33 through a contact hole 37.

Moreover, on the active matrix substrate, a wiring for providing storagecapacity (Cs wiring) 12 is provided in the middle of the pixel electrode4 in the same layer with the gate wirings 1 in the same process as thegate wirings 1. Since Cs on Com method is adopted as the wiring methodof the Cs wirings 12 in the present embodiment, the Cs wirings 12 areall connected to a common wiring.

FIG. 1(b) is a cross-sectional view taken along line A—A of the activematrix substrate incorporated in the liquid crystal display device shownin FIG. 1(a).

As shown in FIG. 1(b), a TFT substrate 10 having the TFT 3 and pixelelectrode 4, and an opposite substrate 20 having an opposite electrode 6are provided so as to face each other through liquid crystal 8.

The following description will explain a structure of the TFT substrate10, beginning with the lowest layer and then upwards. The gate electrode31 branching off from the gate wiring 1 shown in FIG. 1(a) is providedon a transparent insulating substrate 11. A gate insulating film 5 isprovided to cover the gate electrode 31. A semiconductor layer 34 isprovided on the gate insulating film 5 above the gate electrode 31. Achannel protection layer 35 is provided on the center of thesemiconductor layer 34. Two n⁺ layers 36, respectively serving as asource area and a drain area, are provided so as to cover both ends ofthe channel protection layer 35 and a part of the semiconductor layer 34provided on both sides of the channel protection layer 35, and to beseparated from each other on the channel protection layer 35. The n⁺layers 36 are connected respectively to the source electrode 32 and thedrain electrode 33.

An interlayer insulating film 9 is provided to cover the TFT 3 providedin this manner. The pixel electrode 4 is provided on the interlayerinsulating film 9. The pixel electrode 4 is connected to the drainelectrode 33 of the TFT 3 through the contact hole 37 in the interlayerinsulating film 9. An orientation film (not shown) is provided on thepixel electrode 4.

Meanwhile, another orientation film is provided on the oppositeelectrode 6 on the opposite substrate 20. The liquid crystal layer 8 issealed between the TFT substrate 10 and opposite substrate 20, or moreprecisely, between the orientation films provided respectively on theTFT and opposite substrates 10 and 20.

Spacers 7 are provided between the TFT substrate 10 and the oppositesubstrate 20 to maintain the space therebetween. Here, an acrylic resinhaving a Rockwell hardness of M90 is used as the interlayer insulatingfilm 9, and a polystyrene having a Rockwell hardness of M80 is used asthe spacers 7.

Since such a highly transparent acrylic resin is used as the material ofthe interlayer insulating film 9 in the present embodiment, a liquidcrystal display device of excellent display quality with no coloring isobtained. Moreover, the polystyrene used as the material of the spacers7 is softer than the interlayer insulating film 9. Therefore, thespacers 7 do not sink into the TFT substrate 10, thereby keeping thespace between the substrates 10 and 20 constant. Consequently, theliquid crystal display device causing no Newton ring to occur and havinghigh display quality is obtained.

The active matrix substrate of the first embodiment in accordance withthe present invention is configured in the above manner. The followingdescription will explain a manufacturing method of the active matrixsubstrate.

First, the gate wirings 1 (the gate electrode 31), gate insulating film5, semiconductor layer 34, channel protection layer 35 and n⁺ layer 36are formed sequentially with film disposition patterning. The gatewirings 1 (the gate electrode 31) are made of metals, such as Al, Ta andCr: the gate insulating film 5 is made of, for example, SiNx and SiO₂:the semiconductor layer 34 is made of, for example, Si: the channelprotection layer 35 is made of, for example, SiNx. The manufacturingprocess so far is the same as a conventional method of manufacturingactive matrix substrates.

Next, the source wirings 2 (the source electrode 32 and the drainelectrode 33) are formed. In the present embodiment, a two-layeredwiring is provided by forming ITO (Indium Tin Oxide) on a wiring made ofmetals such as Al, Ta and Cr when the above-mentioned members 2, 32 and33 are formed. This enables the wiring to have disconnection redundancy,and mounting terminal portions to have low resistance.

Next, on the source wirings 2, a photosensitive acrylic resin film isformed as the interlayer insulating film 9 with spin coat method to havea thickness of, for example, 3 μm. The film thickness depends onpermittivity of the film made of, for example, the resin. This isbecause a parasitic capacity is caused by the stacking of the wiringsand the pixel electrode 4. Therefore, the permittivity of the resin usedis preferably as low as possible. The resin is then exposed in anecessary pattern and treated with an alkaline solution. Thus, only theexposed part is etched with the alkaline solution, and the contact hole37 is formed through the interlayer insulating film 9.

Here, if the resin can be made photosensitive, the resin is preferablymade photosensitive. This is because if a photosensitive acrylic resinis used, it is possible to perform patterning with photo processingalone. More preferably, a low viscosity resin is used and the resin isdried with prebaking treatment before patterning. More specifically, afilm having a thickness of 3 μm is formed as the interlayer insulatingfilm 9 with spin coat method from a solution including thephotosensitive acrylic resin. For example, an acrylic resin having aviscosity of 29.0 cp is applied at a spin rotation of 900 to 1000 rpm.This makes the interlayer insulating film 9 even, thereby eliminatingroughness conventionally occurring on the pixel electrodes 4. As aresult, undesirable orientation of the liquid crystal is restrained,which improves display quality of the liquid crystal display device.Next, the substrate coated with the above solution is heated up to about100° C. and then solvent for the photosensitive transparent acrylicresin (e.g., ethyl lactate and propylene glycol monomethylether acetate)is dried. The prebaking treatment in this manner improves productivityand prevents bad affection, such as dimensional distortion when theresin really cures.

Resin with poor surface adherence may be improved by making the surfacerough with ashing treatment or light radiation at this stage. If aphotosensitive resin is used as the interlayer insulating film 9, thosetreatments can be carried out at the same time with a process ofremoving residue of the photosensitive resin. In contrast, if anon-photosensitive material is used as the interlayer insulating film 9,the treatments can be carried out at the same time with the photoresistremoving process. Therefore, in either case, the treatments can becarried out without changing the conventional number of manufacturingprocesses of the liquid crystal display device.

The above ashing treatment is carried out in the following manner beforethe pixel electrodes 4 are formed. oxygen plasma treatment is carriedout to the surface of the interlayer insulating film 9 with, forexample, a dry etching device to the depth (film thickness) of 1000 to3000 Å from the surface of the interlayer insulating film 9.

More specifically, for example, the acrylic resin surface receivesashing treatment with a parallel plate plasma etching device at an RFpower of 1.2 kW, a pressure of 800 mTorr, an oxygen flow of 300 sccm, atemperature of 70° C. and an RF application time of 120 sec. Here, theacrylic resin surface is rid of water and carbon dioxide due tooxidation and discomposition of organic substance in the oxygen plasma.As a result, the acrylic resin surface becomes rough. Apart from theabove mentioned dry etching device, dry etching devices of other types,such as of a barrel type and of an RIE (Reactive Ion Etching) type, canalso achieve the same effects in adherence improvement.

Ashing treatment is effective when the interlayer insulating film 9 istreated to the depth of more than 1000 Å from the surface thereof.However, if ashing treatment is carried out too deeply into theinterlayer insulating film 9, the film thickness is decreased by a largeamount, and thus the thickness of the interlayer insulating film 9becomes uneven. As a result, the orientation also becomes disordered,which affects display by the liquid crystal display device. Therefore,ashing treatment is controlled so as to reach the depth of not more than5000 Å, and preferably the depth of not more than 3000 Å.

Meanwhile, specifically, light radiation treatment is carried out by,for example, radiating an ultraviolet ray, such as an excimer ray, tothe surface of the interlayer insulating film 9 in ozone atmosphere. Theradiation makes the surface of the interlayer insulating film 9 rough,and thereby achieving the same effect as the above mentioned ashingtreatment. Note that conditions f or light radiation treatment, such asthe film depth receiving the light radiation, are set in the same manneras ashing treatment.

After the interlayer insulating film 9 is formed with patterning and thecontact hole 37 is formed, the ITO as the pixel electrode 4 is formedwith sputtering method and treated with patterning. The pixel electrode4 is thus connected to the drain electrode 33 of the TFT 3 through thecontact hole 37 in the interlayer insulating film 9.

The TFT substrate 10 manufactured in this manner and the oppositesubstrate 20 on which the opposite electrodes 6 are formed are puttogether, with a sealing member (not shown) maintaining the space of theperipheral portion and the spacers 7 maintaining the space of the otherportions. Then, the liquid crystal layer 8 is enclosed between the twosubstrates. The liquid crystal display device of the first embodiment inaccordance with the present invention is manufactured in this manner.

Here, the acrylic resin having a Rockwell hardness of M90 is used as thematerial of the interlayer insulating film 9, and the polystyrene havinga Rockwell hardness of M80 is used as the material of the spacers 7.However, other materials may be used for the interlayer insulating film9 and the spacer 7 as described in the following.

If the active matrix substrate is incorporated in a transparent typeliquid crystal display device, the interlayer insulating film 9 ispreferably highly transparent, and more specifically an interlayerinsulating film 9 with a transmittance in the visible ray area of morethan 90% is preferred. Here, visibility of a blue color (400 to 500 nm)is slightly inferior to visibility of green and red colors. Therefore,if a material with slight coloring is to be used, considering thatspectral transmittance varies depending on colors, a material having aspectral transmittance as close to 100% as possible for the green andred colors and having a slightly inferior spectral transmittance for theblue color may be used. Therefore, preferred material examples of theinterlayer insulating film 9 of the above-mentioned active matrixsubstrate include polyamide imide (E61 to 74), polyalylate (M87 to 93),polyetherimide (M105 to 109), epoxy (M80 to 110), highly transparentpolyimide (E45 to 58; for example, a composition of diamine and aciddianhydride including hexafluoropropylene).

Meanwhile, if the active matrix substrate is incorporated in such atransparent type liquid crystal display device, the spacers 7 are notnecessary transparent: for example, black-colored spacers may be alsoused. Therefore, the spacers 7 have more material choices than theinterlayer insulating film 9, and may be made of the same material asthe interlayer insulating film 9 or a softer material than theinterlayer insulating film 9.

Moreover, if the active matrix substrate is incorporated in a reflectiontype liquid crystal display device, the interlayer insulating film 9 hasmuch more material choices than in the previous case where the activematrix substrate is incorporated in the transparent type liquid crystaldisplay device. For example, a coloring agent, such as well-known Kapton(trademark of E. I. du Pont de Nemours and Co.) may be used inpolyimide.

[SECOND EMBODIMENT]

A liquid crystal display device of a second embodiment in accordancewith the present invention is basically configured in the same manner asthat of the first embodiment. The only change is that in an activematrix substrate incorporated in the liquid crystal display device ofthe second embodiment, an interlayer insulating film 9 is formed using aresin of a high elastic modulus, especially of high impact resilience.

Here, the liquid crystal display device employing the interlayerinsulating film 9 made of the high impact resilience resin has thefollowing advantage: if pressure is applied on a panel surface (forexample, while the upper and lower substrates are being put together, orwhen the panel is pushed by a finger after the panel is manufactured),the surface of the interlayer insulating film 9 temporarily caves in.However, as the pressure is removed, the surface of the interlayerinsulating film 9 returns to the original state with the elasticity(resilience), and the space between the substrates, which has beendistorted by the pressure, also returns to the original state.

Preferred examples of the resin of a high elastic modulus employed inthe second embodiment in accordance with the present invention includebutadienestyrene copolymer, butyl rubber and fluororubber for thetransparent type liquid crystal display device; and rubber-like elasticmacromolecule, such as polyolefin elastomer and polyurethane rubber, forthe reflection type liquid crystal display device.

[THIRD EMBODIMENT]

FIG. 2 is an enlarged cross-sectional view showing a neighborhood of asealing portion in a liquid crystal display device of a third embodimentin accordance with the present invention. Here, for convenience, membershaving the same function as members illustrated in FIGS. 1(a) and 1(b)are indicated by the same reference numerals and description thereof isomitted.

First, TFT substrate 10 is manufactured in the same manner as in thefirst embodiment. Then as shown in FIG. 2, a part of an interlayerinsulating film 9 under a seal 14 is removed during patterning of theinterlayer insulating film 9. Therefore, gate wirings 1 and a gateinsulating film 5 formed on the gate wirings 1 are provided on atransparent insulating substrate 11 below the seal 14. The interlayerinsulating film 9 and a pixel electrode 4 are stacked on the gatewirings 1 and gate insulating film 5 on the transparent insulatingsubstrate 11 inside the seal 14.

Then, a TFT substrate 10 and an opposite substrate 20 on which oppositeelectrodes 6 are formed are put together, sandwiching the seal 14 with apredetermined space therebetween. The predetermined space is maintainedby spacers 7 and 13. The spacer 13 disposed in the seal 14 is larger indiameter than the spacer 7 disposed in a display area (in a liquidcrystal layer 8).

With this configuration, the problem of inappropriate display in aneighborhood of the seal 14, that is, frequent occurrence of Newtonrings, is solved. If hard substance, such as glass beads, is used as thespacers 13 in the seal 14, the problem is solved more effectively. Thespacers 7 in the display area are preferably, for example, plasticbeads, such as polyimide, epoxy and polystyrene beads. The spacers 7 inthe display area may flow into the seal 14 during the manufacture of theliquid crystal display device. Nonetheless, this does not cause aserious problem.

The adherence of the seal 14 is improved by adding a middle layer 40 tothe liquid crystal display device manufactured in the above-mentionedmanner. As shown in FIG. 3, the middle layer 40 is provided above thetransparent insulating substrate 11 under the seal 14 so as to includesource wirings 2 and ITO therein. The middle layer 40 is also effectivein handling static electricity. Examples of preferred material for thesource wirings 2 and pixel electrodes 4 include metals, nitrides andoxides.

Moreover, foam and the like can be prevented from occurring duringinjection of the liquid crystal layer 8 by a sloping edge of aninterlayer insulating film 9 a formed as shown in FIG. 4. The liquidcrystal 8 can be thus smoothly injected.

The active matrix substrate of the third embodiment in accordance withthe present invention is configured in the above manner. The followingdescription will explain a manufacturing method of the active matrixsubstrate. Explanation of the same processes as in the manufacturingmethod for the first embodiment is omitted.

The same method as the first embodiment is employed from the firstprocess through the process of providing the interlayer insulating film9 on the transparent insulating substrate 11. Next, a contact hole isformed with patterning of the interlayer insulating film 9. A peripheryof the display area, i.e., a part of the interlayer insulating film 9under a portion where the seal 14 is provided is removed during thepatterning of the interlayer insulating film 9 in the same manner as thecontact hole portion is removed. Then, the pixel electrodes 4 areprovided on a portion corresponding to the display area of theinterlayer insulating film 9. An orientation film (not shown) is thendisposed.

The peripheral portions of the TFT substrate 10 manufactured in thismanner and of the opposite substrate 20 on which the opposite electrodes6 are formed are sealed with the seal 14 made from a thermosettingresin, such as an epoxy resin, a photosetting resin and the like. Thespace between the two substrates is kept constant with the spacers 7 and13.

Finally, the last manufacturing processes of the liquid crystal displaydevice of the third embodiment in accordance with the present inventionare to cure the seal 14 and to inject the liquid crystal layer 8.

In the third embodiment in accordance with the present invention, sincethe interlayer insulating film 9 is not provided under the portion wherethe seal 14 is provided, the space between the two substrates does notchange due to curing shrinkage or thermal expansion of the resin formingthe interlayer insulating film 9 when the seal 14 cures.

Moreover, in the third embodiment in accordance with the presentinvention, the gate insulating film 5 is provided under the portionwhere the seal 14 is provided to improve adherence with the seal 14. Atthis time, the seal 14 including the spacers 13 in advance is preferredfor use to improve productivity.

The present invention is explained with the liquid crystal displaydevice adopting Cs on Com method as the wiring method of the wiring forproviding storage capacity (Cs wiring). However, this may be a liquidcrystal display device adopting Cs on Gate method.

As discussed above, the main object of the liquid crystal display deviceof the first through third embodiments is to eliminate the problem ofthe conventional liquid crystal display device, that is, occurrence ofNewton rings observed in a lighting test after injecting the liquidcrystal.

As a step toward achieving the above object, the inventors of thepresent invention conducted researches to pinpoint causes of Newtonrings, and found out that if acrylic resin is used as the interlayerinsulating film 59 and epoxy resin is used as the spacers 57 as in theconventional liquid crystal display device shown in FIG. 5(b), thespacers 57 press the pixel electrode 54, sink into the interlayerinsulating film 59, and thus change the space between the TFT substrate70 and the opposite substrate 71, thereby causing Newton rings to occur.

Despite the fact that the pixel electrodes 54 made of ITO, Al and thelike are formed on the interlayer insulating film 59, the spacers 57still sink. This is likely to be caused by the absolutely thin pixelelectrode 54: the pixel electrode 54 has a thickness of 500 Å to 2000 Å.and the interlayer insulating film 59 has a thickness of 1.5 μm to 4 μm.The same reasoning is likely to apply to the orientation film (notshown).

In this manner, in the conventional liquid crystal display device, thespacer 57 sinking into the interlayer insulating film 59 causes Newtonrings to occur during the lighting test, thereby resulting in adeteriorating defective ratio and reliability.

On the contrary the liquid crystal display devices of the first andsecond embodiments are configured so that the spacers do not sink intothe interlayer insulating film by optimizing the materials of theinterlayer insulating film and spacers. As a result, various problemswith the liquid crystal display device using the resin-made interlayerinsulating film are successfully solved.

Specifically, in the first embodiment, the hardness of the spacers andthe interlayer insulating film are adjusted. The liquid crystal displaydevice of the first embodiment includes: a liquid crystal layer; a firstsubstrate (the opposite substrate 20) provided on one side of the liquidcrystal layer; a second substrate (the TFT substrate 10) provided on theother side of the liquid crystal layer; and a sealing member (the seal14) for sealing the liquid crystal layer between the first and secondsubstrates. The liquid crystal layer has therein at least one firstspacer (the spacer 7) for maintaining a thickness of the liquid crystallayer. The second substrate has: an interlayer insulating film of thesame hardness with the first spacer or a greater hardness than the firstspacer; a pixel electrode disposed on one side of the interlayerinsulating film; at least one switching element (the TFT 3) disposed onthe other side of the interlayer insulating film for controlling adisplay state of a pixel; and a base substrate (the transparentinsulating substrate 11) facing the first substrate through the liquidcrystal layer and the interlayer insulating film.

With the above configuration, the hardness of the interlayer insulatingfilm is either the same as or greater than the hardness of the firstspacer. Therefore, the first spacer can be prevented from sinking in theinterlayer insulating film surface. Newton rings can be thus preventedfrom occurring, which improves reliability and defective ratio inmanufacture of the liquid crystal display device. Moreover, even ifpressure is applied by, for example, a user wiping the liquid crystaldisplay device surface after the liquid crystal display device ismanufactured, the space between the substrates are kept constant. Theliquid crystal display device with high display quality is obtained forthese reasons.

While the interlayer insulating film is formed to have a predeterminedhardness in the first embodiment, the interlayer insulating film of thesecond embodiment is made of elastic body. The second embodiment isconfigured in the same manner as the first embodiment, except that adifferent material is used for the interlayer insulating film. With thisconfiguration, if pressure is applied to the display surface of theliquid crystal display device, the first spacer sinks in the interlayerinsulating film surface and the space between the substrates changestemporarily. Nevertheless, as the pressure is removed, resilient poweroccurs and the space recovers to the predetermined space. Therefore, thespace between the substrates of the liquid crystal display device arekept constant. The liquid crystal display device with good reliability,a low defective ratio and high display quality can be provided for thesereasons in the same manner as in the first embodiment.

In either of the liquid crystal display devices of the first and secondembodiments, the interlayer insulating film is preferably made of resinhaving a transmittance of the visible ray area of not less than 90%.With this configuration, especially if the interlayer insulating film isincorporated in a transparent type liquid crystal display device, it ispossible to obtain beautiful image display with no coloring. Moreover,since transmittance can be prevented from deteriorating, it is possibleto restrain increase of power consumption of the backlight.

Preferred materials with high transmittance for the liquid crystaldisplay device of the first embodiment include polyamide imide,polyalylate, polyetherimide, epoxy and polyimide. Any of these materialscan be used not only for the interlayer insulating film, but also forthe first spacer which requires to be at least as hard as the interlayerinsulating film. Preferred materials for the liquid crystal displaydevice of the second embodiment include butadienestyrene copolymer,butyl rubber and fluororubber.

Meanwhile, if the interlayer insulating film is incorporated in areflection type liquid crystal display device, the transmittance of theinterlayer insulating film is not restricted. Preferred materials forthe first embodiment include a coloring agent, such as Kapton (trademarkof E. I. du Pont de Nemours and Co.). Preferred materials for the secondembodiment include rubber-like elastic macromolecule, such as polyolefinelastomer and polyurethane rubber.

Moreover, in the two embodiments mentioned above, the interlayerinsulating film is preferably made of a photosensitive material. In thiscase, it is possible to perform patterning with photo processing alone,and therefore it is also possible to reduce the number of manufacturingprocesses.

Incidentally, in the two embodiments above, the material for theinterlayer insulating film is restricted in terms of hardness orelasticity, compared with prior art. As a result, there occurs a casewhere only an inferior material to conventional materials in terms ofadherence and the like can be selected to satisfy this point. If amaterial of poor surface adherence is used, and the interlayerinsulating film and the pixel electrode do not adhere to each other, thedistance between the base substrate and the pixel electrode variesundesirably. Therefore, if the liquid crystal is injected and sealedbetween the first substrate (the opposite substrate 20) and the secondsubstrate (the TFT substrate 10) including the base substrate and thepixel electrode, the layer thickness of the liquid crystal layer varies,thereby damaging the display quality. Consequently, if a conventionalmanufacturing method is employed for the liquid crystal display device,such a material of poor surface adherence may not be used as resinforming the interlayer insulating film .

The following description discusses a preferred method of manufacturinga liquid crystal display device when, for example, the material for theinterlayer insulating film does not have desirable adherence asmentioned above. A method of manufacturing a liquid crystal displaydevice including: a pixel electrode and a switching element (the TFT 3)for determining a display state of a pixel; an interlayer insulatingfilm disposed between the switching element and the pixel electrode; anda base substrate (the transparent insulating substrate 11) provided withthe interlayer insulating film, the switching element and the pixelelectrode preferably includes steps of: (1) providing the switchingelement on the base substrate; (2) providing the interlayer insulatingfilm on the switching element; (3) improving film property by making aninterlayer insulating film surface rough; and (4) providing the pixelelectrode on the interlayer insulating film.

The third step includes, for example, a step of ashing treatment orlight radiation in which the interlayer insulating film surface is maderough prior to the fourth step of providing the pixel electrode. As aresult, even if a material of poor surface adherence is used as theresin forming the interlayer insulating film, the interlayer insulatingfilm and the pixel electrode can adhere to each other with no trouble.Note that if the film property improving treatment is ashing treatmentor light radiation treatment, the treatment can be carried out asfollows. If the interlayer insulating film is photosensitive, thetreatment can be carried out at the same time with a process of removingresidue of the photosensitive resin, whereas if the interlayerinsulating film is not photosensitive, the treatment can be carried outat the same time with a process of removing photoresist duringpatterning of the interlayer insulating film. This can avoid an increaseof the number of manufacturing processes, compared with prior art.

Moreover, a method of manufacturing a liquid crystal display deviceincluding: a pixel electrode and a switching element (the TFT 3) fordetermining a display state of a pixel; an interlayer insulating filmdisposed between the switching element and the pixel electrode; and abase substrate (the transparent insulating substrate 11) provided withthe interlayer insulating film, the switching element and the pixelelectrode preferably includes steps of: providing the switching elementon the base substrate; providing the interlayer insulating film on theswitching element; drying the interlayer insulating film with prebakingtreatment before patterning the interlayer insulating film; patterningthe interlayer insulating film; and providing the pixel electrode on theinterlayer insulating film.

With the configuration, the interlayer insulating film is dried withprebaking treatment before pattering of the interlayer insulating film.Therefore, it is possible to prevent bad affection, such as dimensionaldistortion when the resin really cures, and to reduce viscosity of theresin forming the interlayer insulating film. Consequently, it ispossible to improve productivity and dimensional accuracy in manufactureof the liquid crystal display device.

Moreover, the inventors of the present invention studied occurrencefrequency of Newton rings, and confirmed among other things that Newtonrings frequently occur in the sealing portion and that the rings weremore clearly observed with a liquid crystal display device incorporatingan interlayer insulating film in an underlayer of the sealing portion.

In order to prevent occurrence of Newton rings in a neighborhood of thesealing portion, the liquid crystal display device of the thirdembodiment includes: a liquid crystal layer; a first substrate (theopposite substrate 20) provided on one side of the liquid crystal layer;and a second substrate (the TFT substrate 10) having a base substratefacing the first substrate through the liquid crystal layer. On the basesubstrate of the second substrate, a sealing area is provided outsidethe display area, such as in the periphery of the base substrate.Moreover, an interlayer insulating film is provided between the basesubstrate and the liquid crystal layer, except in the sealing area. Atleast one switching element (the TFT 3) for controlling a display stateof a pixel is provided on one side of the interlayer insulating film,whereas the pixel electrode is provided on the other side of theinterlayer insulating film. In addition, the liquid crystal displaydevice includes a sealing member, disposed to be in contact with thesecond substrate in the sealing area, for sealing the liquid crystallayer between the first and second substrates.

If the areas to which the interlayer insulating film is provided includean area where the sealing member and the second substrate are in contactwith each other (such as the portion below the sealing member) as inprior art, there may occur curing shrinkage or thermal expansion withthe resin forming the interlayer insulating film when the resin cures.This causes the space between the first and second substrate to vary andNewton rings to occur, thereby resulting in degradation of the displayquality.

On the contrary, in the above configuration, the interlayer insulatingfilm is not provided in the area where the sealing member and the secondsubstrate are in contact with each other. Therefore, the space betweenthe substrates can be prevented from varying when the sealing membercures. As a result, it is possible to prevent Newton rings to occur in aneighborhood of the sealing member. Besides, the defective ratio andreliability can be improved in manufacture of the liquid crystal displaydevice.

Moreover, the sealing member preferably includes a second spacer, largerthan the first spacer, for maintaining a thickness of the sealingmember. The second spacer can maintain the space between the substrateswith certainty even when the space between the first and secondsubstrates in the sealing area is wider than the other areas by a valueequivalent to the thickness of the interlayer insulating film.Therefore, the varying of the space between the substrates can beprevented, which otherwise would occur with the sealing member, and theoccurrence of Newton rings can be restrained in a neighborhood of thesealing member. Consequently, the liquid crystal display device of highdisplay quality can be realized.

In addition, more preferably, the sealing member includes a secondspacer, having a greater hardness than the first spacer, for maintaininga thickness of the sealing member. With this configuration, the spacebetween the substrates can be maintained with certainty. Consequently,the liquid crystal display device of high display quality can berealized.

In the above-mentioned cases where the sealing member includes thesecond spacer which is at least either larger than the first spacer orhas a greater hardness than the first spacer, it is hoped that thefollowing manufacturing method is adopted. A method of manufacturing aliquid crystal display device including: a liquid crystal layer havingtherein at least one first spacer for maintaining a thickness of theliquid crystal layer; and a sealing member, having a different secondspacer from the first spacer, for sealing the liquid crystal layer witha first substrate and a second substrate disposed on respective sides ofthe liquid crystal layer preferably includes the steps of: (1) includingthe second spacer in the sealing member in advance; and (2) sealing thefirst spacer and a material composing the liquid crystal layer betweenthe first and second substrates with the sealing member including thesecond spacer.

With this configuration, the second spacer disposed in the sealingmember can be prevented from being mixed with the liquid crystal. layer.As a result, the productivity can be improved when the first spacer anda material composing the liquid crystal layer are sealed between thefirst and second substrates with the sealing member. Note that since thefirst spacer is smaller in size or has a smaller hardness than thesecond spacer, even if the first spacer flows into the sealing member,the first spacer does not create a bad affection to the space betweenthe first and second substrates.

In addition, in order to keep the space between the substrates constant,the liquid crystal display device preferably includes a middle film,provided on the sealing area of the base substrate, having betteradherence than the base substrate. With this configuration, theadherence of the sealing member portion is improved, and the highlyreliable liquid crystal display device can be obtained. Moreover, themiddle film is preferably at least one film selected from the groupconsisting of a metallic film, a nitride film and an oxide film. In thiscase, the material for the middle film becomes the same with thematerial for the source wiring of the switching element and the like.Therefore, one process can be shared for forming the switching elementand for forming the middle film, which is especially preferable.

Moreover, the interlayer insulating film in the neighborhood of thesealing area is preferably provided to form a slope so that the sealingarea is thinner than the other area. With this configuration, foam andthe like can be prevented in advance from occurring during injection ofthe liquid crystal, and the liquid crystal can be thus smoothlyinjected.

The invention being thus described, it will be obvious that the same maybe varied in many ways. Such variations are not to be regarded as adeparture from the spirit and scope of the invention, and all suchmodifications as would be obvious to one skilled in the art intended tobe include within the scope of the following claims.

What is claimed is:
 1. A liquid crystal display device comprising: aliquid crystal layer; a first substrate provided on one side of theliquid crystal layer; at least one spacer between the first substrateand a second substrate for maintaining a thickness of the liquid crystallayer; said second substrate including at least one switching elementfor controlling a display state of a pixel, a pixel electrode connectedto one of two ends of the switching element, an interlayer insulatingfilm having a greater hardness than the spacer, the interlayerinsulating film being provided between the switching element and thepixel electrode so as to insulate the other end of the switching elementfrom the pixel electrode, the interlayer insulating film is a resin andhas a thickness of 1.5 μm or greater, and a base substrate facing thefirst substrate through the liquid crystal layer and the interlayerinsulating film; and a sealing member for sealing the liquid crystallayer between the first and second substrates.
 2. The liquid crystaldisplay device as defined in claim 1, wherein the interlayer insulatingfilm is specified to have a flat surface.
 3. The liquid crystal displaydevice as in claim 1, wherein the interlayer insulating film is made ofa resin having a transmittance of a visible ray area of more than 90%.4. The liquid crystal display device as defined in claim 3, wherein theresin is at least one resin selected from the group consisting ofpolyamide imide, polyalylate, polyetherimide, epoxy and polyimide. 5.The liquid crystal display device as defined in claim 1, wherein theinterlayer insulating film and the spacer each have such a hardness thatno Newton rings are produced.
 6. The liquid crystal display device asdefined in claim 1, wherein the interlayer insulating film is made of aphotosensitive material.
 7. A liquid crystal display device as in claim2 wherein said interlayer insulating film has a spectral transmittancefor blue less than for green and red.
 8. A liquid crystal displaydevice, comprising: a liquid crystal layer including therein at leastone spacer for maintaining a thickness of the liquid crystal layer; afirst substrate provided on one side of the liquid crystal layer; asecond substrate including at least one switching element forcontrolling a display state of a pixel, a pixel electrode connected toone of two ends of the switching element, an interlayer insulating filmhaving a Rockwell hardness of E45 or greater, the hardness of saidinterlayer insulating film being greater than a hardness of the spacer,the interlayer insulating film being provided between the switchingelement and the pixel electrode so as to insulate the other end of theswitching element from the pixel electrode, the interlayer insulatingfilm is a resin and has a thickness of at least 1.5 μm, and a basesubstrate facing the first substrate through the liquid crystal layerand the interlayer insulating film; and a sealing member for sealing theliquid crystal layer between the first and second substrates.
 9. Theliquid crystal display device as defined in claim 8, wherein theinterlayer insulating film is specified to have a flat surface.
 10. Theliquid crystal display device as defined in claim 8, wherein theinterlayer insulating film is made of a resin having a transmittance ofa visible ray area of more than 90%.
 11. The liquid crystal displaydevice as defined in claim 10, wherein the resin is at least one resinselected from the group consisting of polyamide imide, polyalylate,polyetherimide, epoxy, and polyimide.
 12. The liquid crystal displaydevice as defined in claim 8, wherein the interlayer insulating film andthe spacer each have such a hardness that no Newton rings are produced.13. The liquid crystal display device as defined in claim 8, wherein theinterlayer insulating film is made of a photosensitive material.
 14. Aliquid crystal display device as in claim 8 wherein said interlayerinsulating film has a spectral transmittance for blue less than forgreen or red.
 15. A liquid crystal display device comprising: a liquidcrystal layer; a first substrate provided on one side of the liquidcrystal layer; at least one spacer between the first substrate and asecond substrate for maintaining a thickness of the liquid crystal layerbetween the first substrate and the second substrate; said secondsubstrate including at least one switching element for controlling adisplay state of a pixel, a pixel electrode connected to one of two endsof the switching element, an interlayer insulating film having the sameor greater hardness than the spacer, the interlayer insulating filmbeing provided between the switching element and the pixel electrode soas to insulate the other end of the switching element from the pixelelectrode, the interlayer insulating film is a resin and has a thicknessof 1.5 μm or greater, and a base substrate facing the first substratethrough the liquid crystal layer and the interlayer insulating film; anda sealing member for sealing the liquid crystal layer between the firstand second substrates.
 16. A liquid crystal display device comprising: aliquid crystal layer; a first substrate provided on one side of theliquid crystal layer; at least one spacer between the first substrateand a second substrate for maintaining a thickness of the liquid crystallayer between the first substrate and the second substrate; said secondsubstrate including at least one switching element for controlling adisplay state of a pixel, a pixel electrode connected to one of two endsof the switching element, an acrylic resin interlayer insulating filmhaving the same or greater hardness than the spacer, the interlayerinsulating film being provided between the switching element and thepixel electrode so as to insulate the other end of the switching elementfrom the pixel electrode, the interlayer insulating film has a thicknessof 1.5 μm or greater, and a base substrate facing the first substratethrough the liquid crystal layer and the interlayer insulating film; anda sealing member for sealing the liquid crystal layer between the firstand second substrates.
 17. A liquid crystal display device, comprising:a liquid crystal layer including therein at least one spacer formaintaining a thickness of the liquid crystal layer; a first substrateprovided on one side of the liquid crystal layer; a second substrateincluding at least one switching element for controlling a display stateof a pixel, a pixel electrode connected to one of two ends of theswitching element, an acrylic resin interlayer insulating film having aRockwell hardness of E45 or greater, the hardness of said interlayerinsulating film being the same as or greater than a hardness of thespacer, the interlayer insulating film being provided between theswitching element and the pixel electrode so as to insulate the otherend of the switching element from the pixel electrode, the interlayerinsulating film is a resin and has a thickness of at least 1.5 μm, and abase substrate facing the first substrate through the liquid crystallayer and the interlayer insulating film; and a sealing member forsealing the liquid crystal layer between the first and secondsubstrates.